There are, of course, many ways of finishing the exteriors of commercial and industrial buildings. One type of external wall system utilizes individual prefabricated panels that are suitably fastened to the building framing, ordinarily by a relatively lightweight retaining system to which the panels can readily be attached and by which the panels are joined to the main building framing. Within this general type of exterior panel wall system are some commercially available versions that utilize composite panels composed of thin aluminum sheets laminated to a plastic core. These composite panels fit into a frame work made up of retainers having grooves that receive the edges of the panels.
These previously known panel systems based on aluminum/plastic/aluminum composite panels have several disadvantages. For one thing the framing system ordinarily requires that the panels and retainers be installed in step, panel by panel and retainer by retainer, working horizontally and vertically, inasmuch as the system depends upon reception of the panel edges in channels or tracks of the retainers. Thus, after a panel is installed, the retainer tracks for the then free edges of the panel are installed and so forth. As far as installation costs are concerned, the assembly procedure is relatively inexpensive and can be accomplished relatively quickly. On the other hand, there is a distinct disadvantage that any panels that might be damaged during the life of the building are difficult to replace. Moreover, the composite panels have shown a tendency to delaminate because of deterioration of the adhesives due to the effect of moisture that attacks the edges where they fit into the retainers.
An exterior building wall panel system should protect the building structure from intrusion of water but also allow the wall to breathe. These two desired characteristics conflict to some degree and are difficult to attain with relatively large panels, because thermal expansion and contraction of the panels is hard on any sealing system. It is quite possible that seals will leak, sometimes as a result of careless installation or, perhaps more commonly, as a result of wear and tear from hundreds or thousands of thermal cycles over a period of years. Water intrusion behind the panel faces due to condensation is inevitable under certain weather conditions.
Construction Specialties, Inc. ("C/S"), the assignee of the present invention, has previously developed and commercialized a wall panel system under the trademark "Techwall" that has numerous advantages over the ones described generally above. Reference may be made to Goertner U.S. patent application Ser. No. 458,540, filed Jan. 17, 1983, and entitled "Panel Wall System" and Bartlett et. al. U.S. Pat. No. 4,506,484, issued Mar. 26, 1985 and entitled "Panel Wall System" for a complete description of the prior art C/S "Techwall" system. The "Techwall" system employs vertical and horizontal retainers that are fastened to the building structure and to which panlike rectangular panels are fastened by clips received in slots in the peripheral flanges and fastened to the retainers. The Goertner application is directed to the panel form and the fastening arrangement. The Bartlett et. al. application discloses a system that employs the concepts of the Goertner panels and fastener clips and provides for water control and drainage and to adapt the Goertner system to the "rain screen" principle of building construction. The "Techwall" system fulfills the objectives referred to above of protecting the building from water intrusion while allowing the wall to breathe and also provides for control and drainage of any water that penetrates the panel facade.